Communications device using measured frequency offset over time to adjust phase and frequency tracking

ABSTRACT

The communications device includes a phase and frequency tracking loop having a signal input and an adjustable loop filter that establishes a predetermined tracking loop bandwidth for samples of communication signals received at the signal input and processed within the tracking loop. A tracking loop update circuit updates loop filter operating parameters and is operative with the loop filter for increasing or decreasing the tracking loop bandwidth of the phase and frequency tracking loop based on the dynamics of the frequency offset of measured samples from the output of the loop filter over time.

FIELD OF THE INVENTION

The present invention relates to communications systems and, moreparticularly, the present invention relates to communications devicesand related systems and methods that track phase and Doppler (orfrequency) error.

BACKGROUND OF THE INVENTION

Some multi-band or other tactical radios and operate in the highfrequency (HF), very high frequency (VHF) (for satellitecommunications), and ultra high frequency (UHF) bands. The range of somemulti-band tactical radios can operate from about 2 through about 512MHz frequency range in some non-limiting examples. The latest generationradios cover about 2.0 to about 2,000 MHz (or higher) to accommodatehigh data rate waveforms and less crowded frequency bands. The highfrequency (HF) transmit mode is governed by standards such asMIL-STD-188-141B, while data modulation/demodulation is governed bystandards such as MIL-STD-188-110B, the disclosures which areincorporated by reference in their entirety.

UHF standards, on the other hand, provide different challenges over the225 to about 512 MHz frequency range, including short-haul line-of-sight(LOS) communication and satellite communications (SATCOM) and cable.This type of propagation can be obtained through different weatherconditions, foliage and other obstacles making UHF SATCOM anindispensable communications medium for many agencies. Differentdirectional antennas can be used to improve antenna gain and improvedata rates on the transmit and receive links. This type of communicationis typically governed in one example by MIL-STD-188-181B, the disclosurewhich is incorporated by reference in its entirety. This standardprovides a family of constant and non-constant amplitude waveforms foruse over satellite links.

The joint tactical radio system (JTRS) is one example of a system thatimplements some of these standards and has different designs that useoscillators, mixers, switchers, splitters, combiners and power amplifierdevices to cover different frequency ranges. The modulation schemes usedfor these types of systems can occupy a fixed bandwidth channel at afixed frequency spectrum. These systems usually utilize a memorylessmodulation, such as phase shift keying (PSK), amplitude shift keying(ASK), frequency shift keying (FSK), quadrature amplitude modulation(QAM), or modulations with memory such as continuous phase modulation(CPM) and may sometimes combine them with a convolutional or other typeof forward error correction (FEC) code. Minimum shift keying (MSK) andGaussian minimum shift keying (GSMK) (together referred to as MSK orGMSK) are a form of continuous phase modulation used in the GlobalSystem for Mobile communications (GSM) and can be used with suchsystems. The circuits used for implementing the MSK waveform couldinclude a continuous phase frequency shift keying (FSK) modulator.

Some of these radios use DAMA satellite communication networks, whichhave enjoyed widespread use in a variety of applications, such as, butnot limited to military environments. In certain military applications,an established requirement issued by the Department of Defense, known asMIL-STD-188-183 and 183A, the disclosure which is hereby incorporated byreference in its entirety, sets forth interoperability standards withwhich (5 KHz and 25 KHz UHF) satellite communication equipment mustconform. A reduced complexity example of such a SATCOM network isdiagrammatically illustrated in FIG. 1 and includes a (geosynchronous)communication satellite 10 and a plurality of (mobile) terrestrialtransceivers/radios 12.

DAMA is a technique that increases the amount of users that a limited“pool” of satellite transponder space can support. The ability to sharebandwidth is based on the theory that not all users will requiresimultaneous access to communication channels. DAMA systems quickly andtransparently assign communication links or circuits based on requestsissued from user terminals to a network control system. When the circuitis no longer in use, the channels are immediately returned to thecentral pool, for reuse by others. By using DAMA, many subscribers canbe served using only a fraction of the satellite resources required bydedicated, point-to-point single-channel-per-carrier networks, thusreducing the costs of satellite networking.

Existing MIL-STD-188-183 and 183A terminals require acquisition anddemodulation of various Phase Shift Keying (PSK) modulation types, suchas Shaped Offset Quadrature Phase Shift Keying (SOQPSK), DifferentialEncoded Quadrature Phase Shift Keying (DEQPSK), and Binary Phase ShiftKeying (BPSK) modulation types. New MIL-STD-188-181C (IntegratedWaveform) requires acquisition and demodulation of Continuous PhaseModulation (CPM) types (in addition to legacy waveforms such as BPSK,DEQPSK, and SOQPSK). The specified preamble phasing sequence for each ofthe modulation types is similar. The required Signal-to-Noise Ratio(SNR) requires advanced signal processing techniques to recover symbolfrequency offset, phase offset, and timing.

Existing DAMA terminals and controllers acquire the modulation preambleby predefining the modem baud rate and correlating for the specificmodem phasing pattern and start-of-message bit sequence. Baud is ameasure of the bit rate, i.e. the number of distinct symbolic changes(signaling event) made to the transmission medium per second in adigitally modulated signal. As each symbol may stand for more than onebit of information, the amount of information sent per second is theproduct of the rate in baud and the number of bits of informationrepresented by each symbol. The baud rate is equal to the symbol ratetimes the number of bits per symbol.

One multiband radio sold under the designation AN/PRC-117F(C) is amultiband, multimission, software-defined radio, for example, the FalconII Manpack from Harris Corporation of Melbourne, Fla. This radio usesBPSK, DEQPSK and the SOQPSK waveforms for DAMA operation. In many ofthese communications systems, DAMA waveforms have a 32 Hz/sec Dopplertracking design objective to allow for airborne operation. In the radioreceiver, the RF circuitry shifts or demodulates an information bearingcomponent of a received signal back to baseband by multiplying it with alocal reference of frequency F_(c). This carrier recovery also is termedphase tracking and must be very accurate to determine data bit valuesrepresented by received symbols. The down-conversion can be difficultbecause of phase variations introduced by Doppler shifting as thetransmitted signal passes through a channel because of the relativemotion between a transmitter and receiver in wireless systems. Also, alocal reference at a transmitter could be out of phase with the localreference at the receiver and the phase error could be time varying.

At lower symbol rates, for example, at 600 and 1,200 symbol rates, thetraditional phase and Doppler (frequency) offset tracking approachessuffer, especially at a lower signal-to-noise (Eb/No) ratio. It has beenfound that the bandwidth of a traditional tracking loop is required tobe wide to track 32 Hz/sec. In some systems, however, this type of widebandwidth tracking loop allows greater noise at lower Eb/No, whichcauses the loop to track off the desired offset.

To overcome these detriments, some communications devices use a phaseestimator as a low pass filter while others have used a phase-lockedloop (PLL) circuit with a tracking bandwidth that is set and based on amaximum offset that is allowed under the circuit and communicationsconditions. The phase-locked loop circuits typically incorporate afilter bandwidth reduction after the signal acquisition.

These approaches provide some remedial effect, but do not alwaysadequately perform under all circumstances and greater enhancements toDoppler (frequency) and phase tracking are desired.

SUMMARY OF THE INVENTION

The communications device includes a phase and frequency tracking loophaving a signal input and an adjustable loop filter that establishes apredetermined tracking loop bandwidth for samples of communicationsignals received at the signal input and processed within the trackingloop. A tracking loop update circuit updates loop filter operatingparameters and is operative with the loop filter for increasing ordecreasing the tracking loop bandwidth of the phase and frequencytracking loop based on the dynamics of the frequency offset of measuredsamples from the output of the loop filter over time.

In one aspect, the tracking loop update circuit includes a frequencyoffset and frequency-delta tracking circuit that is operative fordetermining the dynamics of the frequency offset of measured samplesfrom the loop filter over time. A signal-to-noise ratio estimator canreceive samples of communication signals and estimate thesignal-to-noise level within the communication signals that are outputby the tracking loop. The tracking loop update circuit can update theloop filter operating parameters based on the frequency offset ofmeasured samples from the output of the loop filter over time, themeasured signal-to-noise ratio and the symbol rate of communicationsignal.

In another aspect, the tracking bandwidth within the phase and frequencytracking loop is reduced when the signal-to-noise ratio within receivedsamples of communication signals has been reduced.

A symbol rate configuration circuit can determine the demodulatortracking capabilities based on the symbol rate and can be used by thetracking loop update circuit to update the tracking loop parameters.Also, a burst history circuit can maintain a history of previous signalreception to determine a signal burst history, which can also be used bythe tracking loop update circuit to update tracking loop parameters. Inone aspect, the tracking loop update circuit includes a filter bandwidthlogic circuit connected to the loop filter that calculates the updatedfilter parameters and generates the updated filter parameter to the loopfilter. The phase and frequency tracking loop can be formed as aphased-locked loop circuit that includes a mixer connected to the signalinput, a phase detector that receives signals output from the mixer andconnected to the loop filter and a numerically-controlled oscillatorconnected to the mixer and the output of the loop filter. The trackingloop update circuit can be operative for updating filter parameters fortracking a Demand Assigned Multiple Access (DAMA) waveform. Ademodulator can incorporate the phase and frequency tracking loop andthe tracking loop update circuit in one aspect.

In another aspect, a phase-locked loop circuit and method are set forth.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the detailed description of the invention whichfollows, when considered in light of the accompanying drawings in which:

FIG. 1 is a reduced complexity illustration of a DAMA satellitecommunications network.

FIG. 2 is another example of a satellite communications network usingradio devices with functionality for DAMA communications in accordancewith a non-limiting example of the present invention.

FIG. 3 is a block diagram showing part of a radio communications devicewith a phase-locked loop (PLL) circuit as an adaptive phase andfrequency tracking loop circuit in accordance with a non-limitingexample of the present invention.

FIG. 4 is a graph showing results for a conventional fixed-PLL bandwidthapproach in tracking such as for 600 SYM/SEC SOQPSK.

FIG. 5 is a graph showing results for an adaptive approach thatincorporates the adaptive phase and frequency tracking loop circuit with600 SYM/SEC SOQPSK in accordance with a non-limiting example of thepresent invention.

FIG. 6 is a block diagram of an example of a communications system withvarious communications devices that can be used and modified inaccordance with a non-limiting example of the present invention.

FIG, 7 is a high-level block diagram showing basic components of acommunications device that can be used and modified in accordance with anon-limiting example of the present invention.

FIG. 8 is a perspective view of a portable wireless communicationsdevice as a handheld radio that could incorporate the communicationssystem and radio as a communications device modified to work inaccordance with a non-limiting example of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Different embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsare shown. Many different forms can be set forth and describedembodiments should not be construed as limited to the embodiments setforth herein. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope to those skilled in the art. Like numbers refer to like elementsthroughout.

It should be appreciated by one skilled in the art that the approach tobe described is not limited for use with any particular communicationstandard (wireless or otherwise) and can be adapted for use withnumerous wireless (or wired) communications standards such as EnhancedData rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS)or Enhanced GPRS (EGPRS), extended data rate Bluetooth, Wideband CodeDivision Multiple Access (WCDMA), Wireless LAN (WLAN), Ultra Wideband(UWB), coaxial cable, radar, optical, etc. Further, the invention is notlimited for use with a specific physical layer (PHY) device or radiotype but is applicable to other compatible technologies as well.

Throughout this description, the term communications device is definedas any apparatus or mechanism adapted to transmit, receive or transmitand receive data through a medium. The communications device may beadapted to communicate over any suitable medium such as RF, wireless,infrared, optical, wired, microwave, etc. In the case of wirelesscommunications, the communications device may comprise an RFtransmitter, RF receiver, RF transceiver or any combination thereof.Wireless communication involves: radio frequency communication;microwave communication, for example long-range line-of-sight via highlydirectional antennas, or short-range communication; and/or infrared (IR)short-range communication. Applications may involve point-to-pointcommunication, point-to-multipoint communication, broadcasting, cellularnetworks and other wireless networks.

As will be appreciated by those skilled in the art, a method, dataprocessing system, or computer program product can embody differentexamples in accordance with a non-limiting example of the presentinvention. Accordingly, these portions may take the form of an entirelyhardware embodiment, an entirely software embodiment, or an embodimentcombining software and hardware aspects. Furthermore, portions may be acomputer program product on a computer-usable storage medium havingcomputer readable program code on the medium. Any suitable computerreadable medium may be utilized including, but not limited to, staticand dynamic storage devices, hard disks, optical storage devices, andmagnetic storage devices.

The description as presented below can apply with reference to flowchartillustrations of methods, systems, and computer program productsaccording to an embodiment of the invention. It will be understood thatblocks of the illustrations, and combinations of blocks in theillustrations, can be implemented by computer program instructions.These computer program instructions may be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, implement the functionsspecified in the block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory result in an article of manufacture including instructions whichimplement the function specified in the flowchart block or blocks. Thecomputer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

FIG. 1 shows a satellite communications network that uses a DAMAcontroller 14 and operable with a satellite 10 and two transceivers 12as radio devices. In this particular system, the controller is arack-mounted unit separate from the radio devices. FIG. 1 shows thatsome radio devices that communicate using DAMA incorporate use of a DANAcontroller.

FIG. 2 shows another communications system 20 using transceivers asradio or communications devices 22, 24 that communicate through anantenna with the satellite 26. The radio devices 22, 24 are anintegrated communications device such as a Harris AN/PRC-117F(C) radiothat is operable as a satellite communications radio and includescryptographic capability and operates as an advanced data controller.This radio can operate with various terminals such as portable personalcomputers or ground station that incorporates a data terminal software.

As a non-limiting example of the type of radio communications devicethat can be modified and used in accordance with non-limiting examples,the Harris AN/PRC-117F(C) multiband, multimission, manpack radio is anadvanced software-defined radio, covering the entire 30 to 512 MHzfrequency spectrum. The AN/PRC-117F(C) has embedded CommunicationsSecurity (COMSEC), Transmission Security (TRANSEC) and is fullycompatible with VINSON, ANDVT/KYV-5, KG-84C and 12 kbps fascinatorencryption in voice and data modes with full over-the-air-rekeying(OTAR) capability. The radio can store up to 75 COMSEC keys and supportDS-101, DS102 fill and CT3 interfaces using all common fill devices.

An embedded software programmable JITC certified SATCOM and DemandAssigned Multiple Access (DAMA) modem complies with DODMIL-STD-188-181B, 182-/A, and 183-/A revisions. Mixed Excitation LinearPrediction (MELP) digitized voice improves narrowband voicecommunications and is MIL-STD-3005 compliant with other MELP radios. Aprogrammable SATCOM table can be custom built for international SATCOMrequirements. The system also features SATCOM Situational Awareness(SA).

The AN/PRC-117F(C) radio has SINCGARS and Havequick I/II ECCM frequencyhopping ESIP and ASIP modes that are supported along with ICOM mode 2/3SINCGARS with manual or global positioning system (GPS) and time of day(TOD) clock synchronization capability and SA (Software Acquisition)capability.

A High Performance Waveform (HPW) data waveform can securely transmitand receive email and transfer large files over SATCOM and line of site(LOS) AM/FM nets by adapting to varying channel conditions. HPW ensureserror free data delivery using high-speed, over-the-air data rates up to64 kbps on LOS nets and up to 56 kbps on wideband SATCOM nets. ChannelSCAN provides monitoring of up to 10 SATCOM or LOS nets. Both CDCSS andCTCSS squelch tone support is provided in transmit and receive, for LMRrepeater systems, and FRS nets.

A removable keypad/display unit provides better control when on the movewith a full function remote control capability. A menu-driven interfaceallows programming and control of 100 nets. Cable radio cloning isstandard, or optional wireless radio cloning along with the RadioProgramming Application (RPA) ensure critical communications nets arequickly and accurately programmed and established.

The AN/PRC-117F(C) is a non-limiting example of a radio device that canuse DAMA and communicate by assigning a bandwidth to clients that do notneed require it constantly. DAMA systems assign communication channelsor circuits based on requests issued from user terminals to a networkcontrol system. When the circuit is no longer in use, the channels arethen returned to the central pool for reuse by others. Channels aretypically a pair of carrier frequencies (one for transmit and one forreceive), but can include fixed bandwidth resources such as timeslots ina TDMA burst plan. Once allocated to a pair of nodes, this bandwidth isnot available to other users in the network until their session isfinished. DAMA permits use of one channel (Frequency band, timeslot,etc.) by many users at different times. This technology is mainly usedby small clients as opposed to PAMA (Permanently Assigned MultipleAccess). By using DAMA technology, the amount of users that can use alimited pool of circuits can be greatly increased.

DAMA and PAMA are related only to bandwidth assignment and are not to bemixed with the multiple access methods intended to divide a bandwidthbetween several users at one time, which include FDMA, TDMA, CDMA andothers. These systems typically allow a more deterministic near realtime allocation of bandwidth based on demands and data priority. DAMA iswidely used in satellite communications, especially in VSAT systems.

In accordance with a non-limiting example, a phase and frequencytracking loop circuit, also called adaptive tracking loop such as amodified phase-locked loop circuit, is operative with a tracking loopupdate circuit to update loop filter operating parameters and increaseor decrease the tracking loop bandwidth of the phase and frequencytracking loop based on additional performance metrics and estimates ofchannel parameters as explained in greater detail below. These could bebased on signal-to-noise ratio, symbol rate configuration as data rate,rate of Doppler or frequency change tracking, measured sampled valuesand history of previous receptions as non-limiting examples. It shouldbe understood that each data rate has a different capability in terms oftracking. For example, lower symbol rates (i.e. 600 symbols per second)have more difficulty tracking 32 Hz/sec than higher symbol rates (i.e.2400 symbols per second).

The tracking loop update circuit includes in one aspect asignal-to-noise (Eb/No) estimator that reduces the tracking bandwidthbased on the current symbol rate and on when the signal-to-noise ratiogoes low. This signal-to-noise estimator combined with the currentsymbol rate are part of the tracking loop update circuit which allowstracking of large Doppler (frequency) at high Eb/No while not impairingdemodulator performance of lower Doppler error at low Eb/No. Thetracking loop update circuit can also provide a frequency offset andfrequency-delta tracking for an estimate coherence using dynamics of thefrequency offset and frequency-delta tracking circuit. If the adaptivephase and frequency tracking loop appears to be stabilizing, it canreduce the tracking bandwidth and update the frequency offset estimatebased on the delta or change in frequency history. The tracking loopupdate circuit can also maintain transmission history with a time-outand use previous burst information to aid a current burst. The circuitas described requires cooperation between the PHY (Physical) and MAC(Media Access Control) layers and knowledge concerning the waveformsymbol data rate.

FIG. 3 is a block diagram showing part of a receiver circuit used in theradio communications device indicated generally by the outline at 40.This circuit could be part of a demodulator in a receiver. The circuithas a signal input 41 for received samples of communications signalsprocessed typically by other portions of the RF circuitry that arepassed into a phase-locked loop circuit 42 as the adaptive phase andfrequency tracking loop that includes a mixer 44, numerically-controlledoscillator (NCO) 46, adjustable loop filter 48 and phase detector 50 allin a phase-locked loop configuration shown at 52. As will be explainedbelow, the adjustable loop filter 48 receives updated filter parametersfrom the tracking loop update circuit 60 to increase or decrease thetracking loop bandwidth as necessary. This can be based on thesignal-to-noise ratio, symbol rate, rate of Doppler (frequency) changetracking capability of the waveform, based on measured and sampledvalues over time, plus the history of previous receptions asnon-limiting examples.

The numerically-controlled oscillator (NCO) 46 can be adigitally-controlled oscillator that synthesizes a range of frequenciesfrom a fixed time base and is typically analogous with thevoltage-controlled oscillator (VCO). It could also be avoltage-controlled oscillator driven by a control signal from adigital-to-analog converter. In conjunction with a phase-locked loopanalog frequency synthesizer, it can synthesize precise frequency ratiosand generate spectral sidebands symmetrically on either side of a timebase frequency. It could include a phase accumulator that operatessimilar to a digital waveform generator by incrementing a phase counterby a per-sample increment and a phase-to-amplitude converter such aspart of a memory device where phase values can be looked up in awaveform table to create a sine waveform at a desired phase offset. Adigital-to-analog converter (DAC) can be used to produce an analogwaveform. It can include a digital counter to produce square wavesignals that are accurate.

Part of the received samples after entering the phase and frequencytracking loop circuit 42 are passed into the tracking loop updatecircuit 60 that includes a signal-to-noise estimator 62, which receivesthe samples from the output of the phase and frequency tracking loopcircuit 42. A frequency offset and frequency-delta tracking circuit 64receives feedback signals after filtering in the adjustable loop filter48 as illustrated. Circuit 64 is operative for determining the frequencyoffset of measured samples from the loop filter over time. A filterbandwidth decision logic circuit 66 receives information regarding thesignal-to-noise ratio and the frequency offset and frequency-deltatracking as well as the burst history and symbol rate configuration froma respective burst history circuit 70 and symbol rate configurationcircuit 72. The filter bandwidth decision logic circuit 66 calculatesthe updated filter parameters and passes them to the adjustable loopfilter 48.

The burst history circuit 70 receives data regarding a history ofprevious receptions and maintains a history of previous signalreceptions to determine a signal burst history. The symbol rateconfiguration circuit 72 has apriori knowledge (i.e. a pre-computedlook-up table or a set of rules) of the tracking capabilities of thewaveform demodulator based on the symbol rate and SNR. The informationfrom both circuits can also be used to increase or decrease the trackingbandwidth of the tracking loop circuit 42.

The history of previous receptions can be used for adjusting the loopfilter 48 to aid in tracking bandwidth and processing a currentcommunication signal. Also, it should be understood that the adjustableloop filter can be designed with different circuits. The circuits shownin FIG. 3, including the phase and frequency tracking loop 42 andtracking loop update circuit 60, can be formed as distinct modules orformed monolithically on one integrated circuit or be two separateintegrated circuits. The adjustable loop filter 48 can adjust the ratioof poles as derived from a transfer function. A smaller loop bandwidthcould typically imply that reference spurs are smaller while a largerbandwidth could imply a faster lock time. The loop filter 48 can adjustthe phase margin and increase or decrease the value of attenuation, forexample, it could increase the value of attenuation and obtain a morenarrow bandwidth. The circuit could be designed to change the circuitcapacitance and accomplish a tuning range change of the loop filter.

FIG. 4 is a graph showing results for a conventional circuit using afixed phased-locked loop bandwidth approach with 600 SYMBOLS/SEC SOQPSKand showing different bandwidths. If the wrong tracking is established,this graph illustrates the bit error rate (BER) and the problems thatoccur.

FIG. 5, on the other hand, is a graph showing the results for theadaptive phase and frequency tracking loop circuit using phase andfrequency tracking as a Eb/No and symbol rate based adaptive approachusing the updated filter parameters received into the loop filter 42shown in FIG. 3 with an example of 600 SYM/SEC SOQPSK. The graph showsthe advantageous results with the bit error rate (BER).

Thus, the system and method using the radio communications device andcircuit shown in FIG. 3 allows the additional performance metrics andestimates of channel parameters to adjust the dynamic trackingcapability of the adaptive phase and frequency tracking loop asdescribed. This can provide a performance improvement over many legacyradios.

For purposes of description, some further information on coding,interleaving, and an exemplary wireless, mobile radio communicationssystem that includes ad-hoc capability and can be modified for use isset forth. This example of a communications system that can be used andmodified in accordance with the present invention is now set forth withregard to FIGS. 6 and 7, FIGS. 6 shows a number of radio devices thatcould be transmitters and receivers.

An example of a radio that could be used with such system and method isa Falcon™ III radio manufactured and sold by Harris Corporation ofMelbourne, Fla. This type of radio can support multiple wavebands form30 MHz up to 2 GHz, including L-band SATCOM and MANET. The waveforms canprovide secure IP data networking. It should be understood thatdifferent radios can be used, including software defined radios that canbe typically implemented with relatively standard processor and hardwarecomponents. One particular class of software radio is the Joint TacticalRadio (JTR), which includes relatively standard radio and processinghardware along with any appropriate waveform software modules toimplement the communication waveforms a radio will use. JTR radios alsouse operating system software that conforms with the softwarecommunications architecture (SCA) specification (seewww.jtrs.saalt.mil), which is hereby incorporated by reference in itsentirety. The SCA is an open architecture framework that specifies howhardware and software components are to interoperate so that differentmanufacturers and developers can readily integrate the respectivecomponents into a single device.

The Joint Tactical Radio System (JTRS) Software Component Architecture(SCA) defines a set of interfaces and protocols, often based on theCommon Object Request Broker Architecture (CORBA), for implementing aSoftware Defined Radio (SDR). In part, JTRS and its SCA are used with afamily of software re-programmable radios. As such, the SCA is aspecific set of rules, methods, and design criteria for implementingsoftware re-programmable digital radios.

The JTRS SCA specification is published by the JTRS Joint Program Office(JPO). The JTRS SCA has been structured to provide for portability ofapplications software between different JTRS SCA implementations,leverage commercial standards to reduce development cost, reducedevelopment time of new waveforms through the ability to reuse designmodules, and build on evolving commercial frameworks and architectures.

The JTRS SCA is not a system specification, as it is intended to beimplementation independent, but a set of rules that constrain the designof systems to achieve desired JTRS objectives. The software framework ofthe JTRS SCA defines the Operating Environment (OE) and specifies theservices and interfaces that applications use from that environment. TheSCA OE comprises a Core Framework (CF), a CORBA middleware, and anOperating System (OS) based on the Portable Operating System Interface(POSIX) with associated board support packages. The JTRS SCA alsoprovides a building block structure (defined in the API Supplement) fordefining application programming interfaces (APIs) between applicationsoftware components.

The JTRS SCA Core Framework (CF) is an architectural concept definingthe essential, “core” set of open software Interfaces and Profiles thatprovide for the deployment, management, interconnection, andintercommunication of software application components in embedded,distributed-computing communication systems. Interfaces may be definedin the JTRS SCA Specification. However, developers may implement some ofthem, some may be implemented by non-core applications (i.e., waveforms,etc.), and some may be implemented by hardware device providers.

For purposes of description only, a brief description of an example of acommunications system that includes communications devices thatincorporate the phase and Doppler (frequency) tracking, in accordancewith a non-limiting example, is described relative to a non-limitingexample shown in FIG. 6. This high-level block diagram of acommunications system includes a base station segment and wirelessmessage terminals that could be modified for use with the presentinvention. The base station segment includes a VHF radio 360 and HFradio 362 that communicate and transmit voice or data over a wirelesslink to a VHF net 364 or HF net 366, each which include a number ofrespective VHF radios 368 and HP radios 370, and personal computerworkstations 372 connected to the radios 368,370. Ad-hoc communicationnetworks 373 are interoperative with the various components asillustrated. The entire network can be ad-hoc and include source,destination and neighboring mobile nodes. Thus, it should be understoodthat the HF or VHF networks include HF and VHF net segments that areinfrastructure-less and operative as the ad-hoc communications network.Although UHF and higher frequency radios and net segments are notillustrated, these are included for DAMA and satellite operation

The radio can include a demodulator circuit 362 a and appropriateconvolutional encoder circuit 362 b, block interleaver 362 c, datarandomizer circuit 362 d, data and framing circuit 362 e, modulationcircuit 362 f, matched filter circuit 362 g, block or symbol equalizercircuit 362 h with an appropriate clamping device, deinterleaver anddecoder circuit 362 i modem 362 j, and power adaptation circuit 362 k asnon-limiting examples. A vocoder circuit 3621 can incorporate the decodeand encode functions and a conversion unit could be a combination of thevarious circuits as described or a separate circuit. A clock circuit 362m can establish the physical clock time and through second ordercalculations as described below, a virtual clock time. The network canhave an overall network clock time. These and other circuits operate toperform any functions necessary for the present invention, as well asother functions suggested by those skilled in the art. Other illustratedradios, including all VHF (or UHF) and higher frequency mobile radiosand transmitting and receiving stations can have similar functionalcircuits. Radios could range from 30 MHz to about 2 GHz as non-limitingexamples.

The base station segment includes a landline connection to a publicswitched telephone network (PSTN) 380, which connects to a PABX 382. Asatellite interface 384, such as a satellite ground station, connects tothe PABX 382, which connects to processors forming wireless gateways 386a, 386 b. These interconnect to the UHF, VHF radio 360 or HF radio 362,respectively. The processors are connected through a local area networkto the PABX 382 and e-mail clients 390. The radios include appropriatesignal generators and modulators.

An Ethernet/TCP-IP local area network could operate as a “radio” mailserver. E-mail messages could be sent over radio links and local airnetworks using STANAG-5066 as second-generation protocols/waveforms, thedisclosure which is hereby incorporated by reference in its entiretyand, of course, preferably with the third-generation interoperabilitystandard: STANAG-4538, the disclosure which is hereby incorporated byreference in its entirety. An interoperability standard FED-STD-1052,the disclosure which is hereby incorporated by reference in itsentirety, could be used with legacy wireless devices. Examples ofequipment that can be used in the present invention include differentwireless gateway and radios manufactured by Harris Corporation ofMelbourne, Fla. This equipment could include RF5800, 5022, 7210, 5710,5285 and PRC 117 and 138 series equipment and devices as non-limitingexamples.

These systems can be operable with RF-5710A high-frequency (HF) modemsand with the NATO standard known as STANAG 4539, the disclosure which ishereby incorporated by reference in its entirety, which provides fortransmission of long distance radio at rates up to 9,600 bps. Inaddition to modem technology, those systems can use wireless emailproducts that use a suite of data-link protocols designed and perfectedfor stressed tactical channels, such as the STANAG 4538 or STANAG 5066,the disclosures which are hereby incorporated by reference in theirentirety. It is also possible to use a fixed, non-adaptive data rate ashigh as 19,200 bps with a radio set to ISB mode and an HF modem set to afixed data rate. It is possible to use code combining techniques andARQ.

A communications system that incorporates communications devices can beused in accordance with non-limiting examples of the present inventionand is shown in FIG. 7. A transmitter is shown at 391 and includes basicfunctional circuit components or modules, including a forward errorcorrection encoder 392 a that includes a puncturing module, which couldbe integral to the encoder or a separate module. The decoder 392 a andits puncturing module includes a function for repeating as will beexplained below. Encoded data is interleaved at an interleaver 392 b,for example, a block interleaver, and in many cases modulated atmodulator 392 c. This modulator can map the communications data intodifferent symbols based on a specific mapping algorithm to form acommunications signal. For example, it could form Minimum Shift Keyingor Gaussian Minimum Shift Keying (MSK or GMSK) symbols. Other types ofmodulation could be used in accordance with non-limiting examples of thepresent invention. Up-conversion and filtering occurs at an up-converterand filter 392 d, which could be formed as an integrated module orseparate modules. Communications signals are transmitted, for example,wirelessly to receiver 393.

At the receiver 393, down conversion and filtering occurs at a downconverter and filter 394 a, which could be integrated or separatemodules. The signal is demodulated at demodulator 394 b anddeinterleaved at deinterleaver 394 c. The deinterleaved data (i.e., bitsoft decisions) is decoded and depunctured (for punctured codes),combined (for repeated codes) and passed through (for standard codes) atdecoder 394 d, which could include a separate or integrated depuncturingmodule. The system, apparatus and method can use different modules anddifferent functions. These components as described could typically becontained within one transceiver.

It should be understood, in one non-limiting aspect of the presentinvention, a rate 1/2, K=7 convolutional code can be used as an industrystandard code for forward error correction (FEC) during encoding. Forpurposes of understanding, a more detailed description of basiccomponents now follows. A convolutional code is an error-correctingcode, and usually has three parameters (n, k, m) with n equal to thenumber of output bits, k equal to the number of input bits, and m equalto the number of memory registers, in one non-limiting example. Thequantity k/n could be called the code rate with this definition and is ameasure of the efficiency of the code. K and n parameters can range from1 to 8, m can range from 2 to 10, and the code rate can range from 1/8to 7/8 in non-limiting examples. Sometimes convolutional code chips arespecified by parameters (n, k, L) with L equal to the constraint lengthof the code as L=k (m−1). Thus, the constraint length can represent thenumber of bits in an encoder memory that would affect the generation ofn output bits. Sometimes the letters may be switched depending on thedefinitions used.

The transformation of the encoded data is a function of the informationsymbols and the constraint length of the code. Single bit input codescan produce punctured codes that give different code rates. For example,when a rate 1/2 code is used, the transmission of a subset of the outputbits of the encoder can convert the rate 1/2 code into a rate 2/3 code.Thus, one hardware circuit or module can produce codes of differentrates. Punctured codes allow rates to be changed dynamically throughsoftware or hardware depending on channel conditions, such as rain orother channel impairing conditions.

An encoder for a convolutional code typically uses a look-up table forencoding, which usually includes an input bit as well as a number ofprevious input bits (known as the state of the encoder), the table valuebeing the output bit or bits of the encoder. It is possible to view theencoder function as a state diagram, a tree diagram or a trellisdiagram.

Decoding systems for convolutional codes can use 1) sequential decoding,or 2) maximum likelihood decoding, also referred to as Viterbi decoding,which typically is more desirable. Sequential decoding allows bothforward and backward movement through the trellis. Viterbi decoding asmaximum likelihood decoding examines a receive sequence of given length,computes a metric for each path, and makes a decision based on themetric.

Puncturing convolutional codes is a common practice in some systems andis used in accordance with non-limiting examples of the presentinvention. It should be understood that in some examples a puncturedconvolutional code is a higher rate code obtained by the periodicelimination of specific code bits from the output of a low rate encoder.Punctured convolutional code performance can be degraded compared withoriginal codes, but typically the coding rate increases.

Some of the basic components that could be used as non-limiting examplesof the present invention include a transmitter that incorporates aconvolutional encoder, which encodes a sequence of binary input vectorsto produce the sequence of binary output vectors and can be definedusing a trellis structure. An interleaver, for example, a blockinterleaver, can permute the bits of the output vectors. The interleaveddata would also be modulated at the transmitter (by mapping to transmitsymbols) and transmitted. At a receiver, a demodulator demodulates thesignal.

A block deinterleaver recovers the bits that were interleaved. A Viterbidecoder could decode the deinterleaved bit soft decisions to producebinary output data.

Often a Viterbi forward error correction module or core is used thatwould include a convolutional encoder and Viterbi decoder as part of aradio transceiver as described above. For example if the constraintlength of the convolutional code is 7, the encoder and Viterbi decodercould support selectable code rates of 1/2, 2/3, 3/4, 4/5, 5/6, 6/7, 7/8using industry standard puncturing algorithms.

Different design and block systems parameters could include theconstraint length as a number of input bits over which the convolutionalcode is computed, and a convolutional code rate as the ratio of theinput to output bits for the convolutional encoder. The puncturing ratecould include a ratio of input to output bits for the convolutionalencoder using the puncturing process, for example, derived from a rate1/2 code.

The Viterbi decoder parameters could include the convolutional code rateas a ratio of input to output bits for the convolutional encoder. Thepuncture rate could be the ratio of input to output bits for theconvolutional encoder using a puncturing process and can be derived froma rate 1/2 mother code. The input bits could be the number of processingbits for the decoder. The Viterbi input width could be the width ofinput data (i.e. soft decisions) to the Viterbi decoder. A metricregister length could be the width of registers storing the metrics. Atrace back depth could be the length of path required by the Viterbidecoder to compute the most likely decoded bit value. The size of thememory storing the path metrics information for the decoding processcould be the memory size. In some instances, a Viterbi decoder couldinclude a First-In/First-Out (FIFO) buffer between depuncture andViterbi function blocks or modules. The Viterbi output width could bethe width of input data to the Viterbi decoder.

The encoder could include a puncturing block circuit or module as notedabove. Usually a convolutional encoder may have a constraint length of 7and take the form of a shift register with a number of elements, forexample, 6. One bit can be input for each clock cycle. Thus, the outputbits could be defined by a combination of shift register elements usinga standard generator code and be concatenated to form an encoded outputsequence. There could be a serial or parallel byte data interface at theinput. The output width could be programmable depending on the puncturedcode rate of the application.

A Viterbi decoder in non-limiting examples could divide the input datastream into blocks, and estimate the most likely data sequence. Eachdecoded data sequence could be output in a burst. The input andcalculations can be continuous and require four clock cycles for everytwo bits of data in one non-limiting example. An input FIFO can bedependent on a depuncture input data rate.

It should also be understood that the radio device is not limited toconvolutional codes and similar FEC, but also turbo codes could be usedas high-performance error correction codes or low-density parity-checkcodes that approach the Shannon limit as the theoretical limit ofmaximum information transfer rate over a noisy channel. Thus, someavailable bandwidth can be increased without increasing the power of thetransmission. Instead of producing binary digits from the signal, thefront-end of the decoder could be designed to produce a likelihoodmeasure for each bit.

The system, in accordance with non-limiting examples of the presentinvention, can be used in multiprocessor embedded systems and relatedmethods and also used for any type of radio software communicationsarchitecture as used on mainframe computers or small computers,including laptops with an added transceiver, such as used by militaryand civilian applications, or in a portable wireless communicationsdevice 420 as illustrated in FIG. 8. The portable wirelesscommunications device is illustrated as a radio that can include atransceiver as an internal component and handheld housing 422 with anantenna 424 and control knobs 426. A Liquid Crystal Display (LCD) orsimilar display can be positioned on the housing in an appropriatelocation for display. The various internal components, including dualprocessor systems for red and black subsystems and software that isconforming with SCA, is operative with the illustrated radio. Although aportable or handheld radio is disclosed, the architecture as describedcan be used with any processor system operative with the system inaccordance with non-limiting examples of the present invention. Anexample of a communications device that could incorporate thecommunications system in accordance with non-limiting examples of thepresent invention, is the Falcon® III manpack or tactical radio platformmanufactured by Harris Corporation of Melbourne, Fla.

This application is related to copending patent applications entitled,“COMMUNICATIONS DEVICE USING MEASURED SIGNAL-TO-NOISE RATIO TO ADJUSTPHASE AND FREQUENCY TRACKING,” which is filed on the same date and bythe same assignee and inventors, the disclosure which is herebyincorporated by reference.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1. A communications device, comprising: a phase and frequency trackingloop having a signal input and an adjustable loop filter thatestablishes a predetermined tracking loop bandwidth for samples ofcommunications signals received at the signal input and processed withinthe tracking loop; and a tracking loop update circuit that updates loopfilter operating parameters and operative with the loop filter forincreasing or decreasing the tracking loop bandwidth of the phase andfrequency tracking loop based on the dynamics of the frequency offset ofmeasured samples from the output of the loop filter over time.
 2. Thecommunications device according to claim 1, wherein said tracking loopupdate circuit further comprises a frequency offset and frequency-deltatracking circuit that is operative for determining the frequency offsetof measured samples from the loop filter over time.
 3. Thecommunications device according to claim 1, wherein said tracking loopupdate circuit further comprises a signal-to-noise ratio estimator thatreceives the samples of communications signals and estimates thesignal-to-noise level within the communications signals that are outputby the tracking loops and said tracking loop update circuit updates loopfilter operating parameters based on the dynamics of the frequencyoffset of measured samples from the output of the loop filter over timeand the measured signal-to-noise ratio.
 4. The communications deviceaccording to claim 3, wherein the tracking bandwidth within the phaseand frequency tracking loop is reduced when the signal-to-noise ratiowithin received samples of communications signals has been reduced. 5.The communications device according to claim 1, wherein the trackingloop update circuit further comprises a symbol rate configurationcircuit that is operative for determining the tracking capabilities ofthe demodulator based on the symbol rate, and said tracking loop updatecircuit updates the tracking loop parameters based on the dynamics offrequency offset of measured samples from the output of the loop filterover time and the current demodulator tracking capability.
 6. Thecommunications device according to claim 1, wherein said tracking loopupdate circuit further comprises a burst history circuit that isoperative for maintaining a history of previous signal receptions todetermine a signal burst history, and said tracking loop update circuitupdates the tracking loop parameters based on the dynamics of thefrequency offset of measured samples from the output of the loop filterover time and the signal burst history.
 7. The communications deviceaccording to claim 1, wherein the tracking loop update circuit furthercomprises a filter bandwidth logic circuit connected to the loop filterthat calculates the updated filter parameters and generates the updatedfilter parameters to the loop filter.
 8. The communications deviceaccording to claim 1, wherein said phase and frequency tracking loopcomprises a phase-locked loop circuit.
 9. The communications deviceaccording to claim 8, wherein said phase-locked loop circuit furthercomprises a mixer connected to the signal input, a phase detector thatreceives signals output from the mixer and connected to the loop filter,and numerically controlled oscillator connected to the mixer and theoutput of the loop filter.
 10. The communications device according toclaim 1, wherein said tracking loop update circuit is operative forupdating filter parameters for tracking a Demand Assigned MultipleAccess (DAMA) waveform.
 11. The communications device according to claim1, and further comprising a demodulator that incorporates the phase andfrequency tracking loop and the tracking loop update circuit.
 12. Aphase-locked loop circuit in a communications device, comprising: asignal input; a mixer connected to the signal input; a phase detectorthat receives signals output from the mixer; a loop filter connected tothe phase detector that establishes a predetermined tracking loopbandwidth for samples of communications signals received at the signalinput and processed within the phase-locked loop; a numericallycontrolled oscillator connected to the mixer and the output of the loopfilter; and a loop update circuit comprising a frequency offset andfrequency-delta tracking circuit operative for determining the dynamicsof the frequency offset of measured samples from the loop filter overtime and a filter bandwidth logic circuit connected to the loop filterand frequency offset and frequency-delta tracking circuit thatcalculates updated filter parameters and generates the updated filterparameters to the loop filter for increasing or decreasing the trackingloop bandwidth based on the dynamics of the frequency offset of measuredsamples from the loop filter over time.
 13. The phase-locked loopcircuit according to claim 12, wherein said loop update circuit furthercomprises a symbol rate configuration circuit connected to the filterbandwidth logic circuit and operative for determining the trackingcapability of the demodulator based on the symbol rate, and said filterbandwidth logic circuit calculates updated filter parameters based onthe dynamics of the frequency offset of measured samples from the loopfilter over time and the current tracking capability of the demodulator.14. The phase-locked loop circuit according to claim 12, wherein saidloop update circuit further comprises a signal-to-noise ratio estimatorconnected to the filter bandwidth logic circuit and operative forreceiving the samples of communications signals and estimating the noiselevel within the communications signals, and said filter bandwidth logiccircuit calculates updated filter parameters based on the measuredsignal-to-noise ratio and the dynamics of the frequency offset ofmeasured samples from the loop filter over time.
 15. The phase-lockedloop circuit according to claim 14, wherein the tracking bandwidth isreduced when the signal-to-noise ratio within received samples ofcommunications signals has been reduced.
 16. The phase-locked loopcircuit according to claim 14, wherein said loop update circuit furthercomprises a burst history circuit connected to the filter bandwidthlogic circuit and operative for maintaining a history of previous signalreceptions to determine a signal burst history, and said filterbandwidth logic circuit calculates updated filter parameters based onthe dynamics of the frequency offset of measured samples from the loopfilter over time and the signal burst history.
 17. A method ofcommunicating data, comprising: receiving a communications signal withina phase and frequency tracking loop having an adjustable loop filter;establishing a predetermined tracking loop bandwidth for samples ofreceived communications signals processed within the tracking loop;determining the dynamics of the frequency offset of measured samplesfrom the loop filter over time; and updating loop filter operatingparameters to increase or decrease the tracking loop bandwidth of thephase and frequency tracking loop based on the dynamics of the frequencyoffset of measured samples from the loop filter over time.
 18. Themethod according to claim 17, which further comprises determining thetracking capability of the demodulator based on the symbol rate, and thetracking loop update circuit updates the tracking loop parameters basedon the dynamics of the frequency offset of measured samples from theloop filter over time and the current tracking capability of thedemodulator.
 19. The method according to claim 17, which furthercomprises maintaining a history of previous signal receptions todetermine a signal burst history, and the tracking loop update circuitupdates the tracking loop parameters based on the dynamics of thefrequency offset of measured samples from the loop filter over time andthe signal burst history.
 20. The method according to claim 17, whichfurther comprises determining the signal-to-noise level within thecommunications signals that are input to the tracking loop, and thetracking loop update circuit updates loop filter operating parametersbased on the measured signal-to-noise ratio and the dynamics of thefrequency offset of measured samples from the loop filter over time. 21.The method according to claim 20, which further comprises reducing thetracking bandwidth within the phase and frequency tracking loop when thesignal-to-noise ratio within received samples of communications signalshas been reduced.
 22. The method according to claim 17, which furthercomprises updating filter parameters for tracking a Demand AssignedMultiple Access (DAMA) waveform.
 23. The method according to claim 17,which further comprises processing the communications signals within aphase-locked loop circuit comprising a mixer connected to the signalinput, a phase detector that receives signals output from the mixer andconnected to the loop filter, and numerically controlled oscillatorconnected to the mixer and the output of the loop filter.